ui: Refactor data-attrs constants, enum for bool strings (#27002)

* refactor: Data-attribute constants + boolean string enum

* refactor: Use CSS class string constants

* refactor: Address review comments

tools/ui/tests/client/chat-form-enter-code-block.svelte.test.ts

@@ -2,7 +2,7 @@
 // fenced-code-block flow: while the caret sits inside a fenced
 // block region - closed, or still OPEN while the user is typing
 // one - plain Enter adds a line instead of submitting the message.
-// The textarea path is covered here end-to-end (the contenteditable
+// The textarea path is covered here end-to-end (the ChatFormInputRich
 // consumes the same case locally; see chat-form-input-rich).
 
 import ChatFormTestWrapper from './components/ChatFormTestWrapper.svelte';

tools/ui/tests/client/chat-form-input-rich-blocks.svelte.test.ts

@@ -1,4 +1,4 @@
-// Guards the newline contract of the chat-form contenteditable: browsers
+// Guards the newline contract of the ChatFormInputRich: browsers
 // restructure the flat DOM on Enter (`<div>` wrappers, `<br>` shapes) and
 // serialization must fold those back into `\n` so the emitted value never
 // diverges from what is on screen.
@@ -13,7 +13,7 @@ const SOURCE = 'see [docs](file:///a/b) here';
 function editableIn(container: HTMLElement): HTMLElement {
 	const el = container.querySelector('[role="textbox"]');
 
-	if (!(el instanceof HTMLElement)) throw new Error('contenteditable not rendered');
+	if (!(el instanceof HTMLElement)) throw new Error('ChatFormInputRich not rendered');
 
 	return el;
 }

tools/ui/tests/client/chat-form-input-rich-undo.svelte.test.ts

@@ -1,4 +1,4 @@
-// Guards the editing-key contract of the chat-form contenteditable:
+// Guards the editing-key contract of the ChatFormInputRich:
 // undo/redo is replayed from source snapshots (the token rebuilds destroy
 // the native undo stack), and Tab is NOT intercepted (WCAG 2.1.2 no
 // keyboard trap), matching the plain textarea.
@@ -13,7 +13,7 @@ const SOURCE = 'see [docs](file:///a/b)';
 function editableIn(container: HTMLElement): HTMLElement {
 	const el = container.querySelector('[role="textbox"]');
 
-	if (!(el instanceof HTMLElement)) throw new Error('contenteditable not rendered');
+	if (!(el instanceof HTMLElement)) throw new Error('ChatFormInputRich not rendered');
 
 	return el;
 }

tools/ui/tests/client/chat-form-input-rich.svelte.test.ts

@@ -1,4 +1,4 @@
-// Guards the clipboard contract of the chat-form contenteditable:
+// Guards the clipboard contract of the ChatFormInputRich:
 // copy/cut expose the markdown SOURCE of the selection (each badge
 // contributes its full `[name](file://...)` link) and pasting such
 // markdown re-renders the badges.
@@ -16,7 +16,7 @@ const BADGE_SELECTOR = '[data-mention-badge="true"]';
 function editableIn(container: HTMLElement): HTMLElement {
 	const el = container.querySelector('[role="textbox"]');
 
-	if (!(el instanceof HTMLElement)) throw new Error('contenteditable not rendered');
+	if (!(el instanceof HTMLElement)) throw new Error('ChatFormInputRich not rendered');
 
 	return el;
 }

tools/ui/tests/client/chat-form-mention-picker-gate.svelte.test.ts

@@ -3,7 +3,7 @@
 // it, the picker still opens but explains why instead of firing searches
 // that would only fail with "Search failed".
 
-import ChatFormMentionPicker from '$lib/components/app/chat/ChatForm/ChatFormPickers/ChatFormPickerMention.svelte';
+import ChatFormPickerMention from '$lib/components/app/chat/ChatForm/ChatFormPickers/ChatFormPickerMention.svelte';
 import { DISABLED_TOOL_KEYS_LOCALSTORAGE_KEY } from '$lib/constants';
 import { BuiltInTool } from '$lib/enums';
 import { toolsStore } from '$lib/stores/tools.svelte';
@@ -25,7 +25,7 @@ function setBuiltinTools(defs: OpenAIToolDefinition[]) {
 }
 
 function renderPicker() {
-	return render(ChatFormMentionPicker, {
+	return render(ChatFormPickerMention, {
 		isOpen: true,
 		onClose: () => {},
 		onSelect: () => {},
@@ -39,7 +39,7 @@ afterEach(() => {
 	localStorage.removeItem(DISABLED_TOOL_KEYS_LOCALSTORAGE_KEY);
 });
 
-describe('ChatFormMentionPicker file_glob_search gate', () => {
+describe('ChatFormPickerMention file_glob_search gate', () => {
 	it('explains that file search is unavailable when the server has no tools', async () => {
 		setBuiltinTools([]);
 		renderPicker();